1. Field of the Invention
This invention relates to a diaphragm type air spring, and more particularly to an improvement of a diaphragm type differential air spring provided with two large and small air chambers.
2. Description of the Prior Art
Since an air spring of this type produces a large vibration damping force even at a small size, there have been proposed various structures for the air spring. These known air springs are roughly classified into a diaphragm type and a bellows type. They have advantages in that they produce the vibration damping force through the function thereof is the same as in metal springs and rubber springs, and that they are soft as compared with the metal and rubber springs and hence the spring height, load bearing capacity and spring constant can individually be set in the spring design. Therefore, these air springs are widely applied to various vibration systems such as industrial machines, automobiles, railway vehicles and the like for the purpose of vibration insulation and cushioning.
Moreover, it is known that the vibration damping force of the air spring is largely influenced by external factors such as speed, frequency and the like of vibration transmitted to the air spring as well as internal factors such as air flowing amount inside the air spring, air flow rate and the like.
In order to bring about an increase of the vibration damping force by increasing the air flowing amount, particularly exerted on the vibration damping force by the above described internal factors, therefore, it has hitherto been attempted to connect a flexible air spring to an auxiliary tank through an orifice to thereby permit the flow of air between them.
According to this prior art, however, the air flowing amount inside the air spring is determined only by the change of pressure inside the air spring, i.e. the difference in pressure between the air spring and the auxiliary tank. For example, when the enclosed internal pressure P of the air spring is increased to P+.DELTA.P by the compression deformation of the air spring, air merely flows from the air spring into the auxiliary tank until the pressure increment .DELTA.P spreads into the inside of the auxiliary tank not subjected to the deformation or still holding the internal pressure P in the compression deformation of the air spring so that the internal pressure of each of the air spring and the auxiliary tank becomes equal to P+.DELTA.P.sub.0 (wherein .DELTA.P.sub.0 is less than .DELTA.P). Therefore, such a combination of the air spring and the auxiliary tank cannot provide a large vibration damping force. Nevertheless, if it is intended to obtain a relatively large vibration damping force, the volume of the auxiliary tannk must be enlarged considerably, which create problems in the cost and installation space.
Further, it is confirmed from experiments that the limit of the present increment .DELTA.P to the enclosed internal pressure P of the air spring and auxiliary tank is .DELTA.P.sub.max =0.1.about.0.3P. In case of the air spring provided with a small size auxiliary tank, therefore, it is actually impossible to obtain a large vibration damping force.